I have a 75 gallon tank that's set up as freshwater. It was previously used as a saltwater tank. It was cleaned out, but not as well as I would like because I live in an apartment and don't have access to a hose. I put some tetra's I got from pet-smart for 1 in there to help it cycle, and they immediately died. I tested the water, and the ammonia, ph, nitrates, and nitrates were all in the normal ranges. The only idea I can think of is there was still salt left in the tank, would this cause the fish to die? Any help would be great.